Re: [GSoC PATCH 1/1] diff: improve scaling of filenames in diffstat to handle UTF-8 chars
From: Junio C Hamano <hidden>
Date: 2026-01-14 22:50:06
LorenzoPegorari [off-list ref] writes:
The `show_stats()` function tries to scale the filenames in the diffstat to
ensure they don't exceed the given `name-width`. It does so by calculating
the "display width" of the characters to be dropped, but then advances the
filename pointer by that number of bytes.
However, the "display width" of a character is not always equal to its byte
count. The result is that sometimes, when displaying UTF-8 characters,
filenames exceed the given `name-width`, and frequently the bytes of the
UTF-8 characters are truncated.
The following is an example of the issue, where the 2 files are "HelloHi" and
"Hello你好", and `name-width=6`:
...oHi | 0
...<BD><A0>好 | 0
Make the filename pointer move by the actual number of bytes of the
characters to drop from the filename, rather than their display width, using
the `utf8_width()` function.
Signed-off-by: LorenzoPegorari <redacted>
---
diff.c | 15 ++++-----------
1 file changed, 4 insertions(+), 11 deletions(-)Two comments and a half. * The change needed for this is surprisingly simple. * You already know about samples that may exhibit the issue you are addressing. Can we add it as a test case somewhere in t/ directory? * The NEEDSWORK item addressed by this patch is one of the two NEEDSWORK items added by ce8529b2 (diff: leave NEEDWORK notes in show_stats() function, 2022-10-21). Makes me wonder how involved the changes would need to be to solve the other one? Thanks.
quoted hunk
diff --git a/diff.c b/diff.c index a68ddd2168..271ace5728 100644 --- a/diff.c +++ b/diff.c@@ -2859,17 +2859,10 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options) char *slash; prefix = "..."; len -= 3; - /* - * NEEDSWORK: (name_len - len) counts the display - * width, which would be shorter than the byte - * length of the corresponding substring. - * Advancing "name" by that number of bytes does - * *NOT* skip over that many columns, so it is - * very likely that chomping the pathname at the - * slash we will find starting from "name" will - * leave the resulting string still too long. - */ - name += name_len - len; + + while (name_len > len) + name_len -= utf8_width((const char**)&name, NULL); + slash = strchr(name, '/'); if (slash) name = slash;